Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

2. The capillary tube, as an expansion device, is used in

Domestic refrigerators

Room air conditioners

All of these

Water coolers

3. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

4. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

5. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Less

Same

6. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

7. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Zero

Positive

None of these

8. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

9. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Condenser and receiver

Compressor and condenser

Evaporator and compressor

10. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Ericson

Stirling

Carnot

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11. For obtaining high COP, the pressure range of compressor should be

Optimum

Any value

Low

High

12. Rating of a domestic refrigerator is of the order of

40 tons

10 tons

5 tons

0.1 ton

13. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Superheat the vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

14. The freezing point of sulphur dioxide is

-77.7°C

-135.8°C

-75.2°C

-56.6°C

15. Most thermostatic expansion valves are set for a superheat of

10°C

15°C

20°C

5°C

16. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

2 bar

8 bar

30 bar

17. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Any one of the above

Equal to unity

Always more than unity

18. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 3

1: 9

1: 1

19. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.4

0.6

0.376

20. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

4.33

2.33

3.33

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21. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

22. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

23. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Axial

Centrifugal

Miniature sealed unit

24. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

25. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

26. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant pressure

Involves no change in volume

Takes place at constant entropy

27. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

28. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Freon

Brine

Ammonia

29. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Wet bulb temperature

Relative humidity

Dew point temperature

30. The boiling point of ammonia is

-10.5°C

-30°C

-33.3°C

-77.7°C

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31. A bootstrap air cooling system has

Four heat exchangers

One heat exchanger

Three heat exchangers

Two heat exchangers

32. Freon group of refrigerants are

Inflammable

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

33. Which of the following is not a desirable property of a refrigerant?

Large latent heat

High risibility with oil

Good electrical conductor

Low boiling point

34. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

Water will never evaporate

A gas will never liquefy

35. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Super-cooling

Sub-cooling or under-cooling

None of these

36. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Absorber

Condenser

Evaporator

37. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

At critical Temperature

38. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Rankine

Reversed Carnot

Carnot

39. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Condenser tubes

Refrigerant cooling tubes

Capillary tubes

40. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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